1. Field of the Invention
The present invention relates to a rack driving-type power assisted steering apparatus. More particularly, the present invention relates to a rack driving-type power assisted steering apparatus, which can prevent a lock screw from being loosened due to vibration in axial and radial directions generated by a rack bar, a ball nut, and a rack housing when the rack bar slides while the ball nut rotates, reduce vibration and noise of the ball nut and the rack bar transferred through a bearing, and provide a driver with steering comfortability.
2. Description of the Prior Art
A power assisted steering apparatus of a vehicle has generally adopted a hydraulic power steering apparatus using hydraulic power of a hydraulic power pump. However, an electric power steering apparatus using a motor has been gradually and widely used recently.
A general electric power steering apparatus generally includes a steering system extending from a steering wheel to wheels in both sides and an auxiliary power mechanism for supplying auxiliary steering power to the steering system.
The auxiliary power mechanism includes a torque sensor for sensing steering torque applied to the steering wheel by the driver and outputting an electric signal proportional to the sensed steering torque, an Electric Control Unit (ECU) for generating a control signal based on the electric signal transferred from the torque sensor, a motor for generating auxiliary steering power based on the control signal transferred from the ECU, and a belt-type electric power apparatus for transferring auxiliary power generated in the motor to the rack bar through a belt.
FIG. 1 is a partial sectional view schematically illustrating a rack driving-type power assisted steering apparatus according to a prior art and FIG. 2 is a sectional view schematically illustrating a part of the rack driving-type power assisted steering apparatus according to the prior art.
As illustrated in FIGS. 1 and 2, the rack driving-type power assisted steering apparatus according to the prior art includes a rack bar 140 extending in a transverse direction of a vehicle and including a rack gear formed at one side of an outer peripheral surface of the rack bar 140, a pinion shaft 110 including a pinion gear engaged with the rack gear, a ball nut 210 engaged with an outer peripheral screw groove 145 through balls 220, a belt-type electric power apparatus 160 for connecting the ball nut 210 and a motor shaft 155, and a motor 150.
The pinion shaft 110 is connected to a steering wheel through a steering shaft, and the rack bar 140 provided with the outer peripheral screw groove 125 having a predetermined length at one side of an outer peripheral surface of the rack bar is embedded in a rack housing 120.
The belt-type electric power apparatus 160 includes the belt for connecting the motor shaft 155 and the ball nut 210 and transfers the auxiliary steering power generated by the motor 150 proportional to the steering torque applied to the steering wheel to the rack bar 140 through the ball nut 210.
As illustrated in FIG. 2, the rack driving-type power assisted steering apparatus according to the prior art includes the rack bar 140 provided with the outer peripheral screw groove 145 at the outer peripheral surface thereof, the ball nut 210 provided with a center path 215 for circulation of balls 220, the balls 220 rolling while being in contact with the outer peripheral screw groove 145 and the center path 215 of the rack bar 140, and an end cap 230 attached to a distal end of the ball nut 210.
In the rack driving-type power assisted steering apparatus, the rack bar 140 slides according to the rolling movement of the balls 220 while the balls 220 are in contact with the outer peripheral screw groove 145 of the rack bar 140 and an inner peripheral screw groove of the ball nut 210.
However, the rack driving-type power assisted steering apparatus according to the prior art has a problem in that noise and vibration are generated through the rack bar, the ball nut, the bearing, and the rack housing when the rack bar slides while the ball nut rotates, and the generated noise and vibration are transferred to other components to cause coupled components to become loosened.
Further, the transferred noise and vibration are transferred to the driver together with vibration and noise of other components, thereby decreasing steering comfortability of a driver.